>The question is how similar they are. They both use the 16550 chips so any
>differences are likely to lie in the address mapping of the serial chips
>and any interrupt control logic. If this information can be determined

Linux has a driver for the Dual Serial card.  I think it works, though I 
haven't tried it recently.  You should be able to derive enough hardware 
information from that to get one going.

p.